The invention related to a hydraulic function-performing unit having a main housing and at least one movable function-performing element, the position and/or movement of which in the main housing determines flow and/or pressure conditions and/or chamber volumes for hydraulic fluid, and having at least one sensor.
Hydraulic function-performing units which come into consideration include, for example, valves, especially proportional valves, in which the function-performing element is formed by the valve member, a main slide valve or a compensating slide valve. Here, the control of the movement or the position of at least one function-performing element is often effected externally, and in some cases only indirectly. The function-performing unit may, however, also be in the form of an actuating unit, for example a piston-cylinder unit. The function-performing element, the piston, is here displaced by the hydraulic fluid.
U.S. Pat. No. 4,796,661 discloses the incorporation of a pressure sensor in a proportional electro-hydraulic pressure control valve, the sensor delivering an electrical output signal which can be used to indicate the controlled pressure numerically or to effect control of the current of a magnet which in its turn is responsible for the position of the valve member in the valve housing.
Furthermore, it is known from an electronic load sensing system "E.LS.A" of the firm Barmag AG, Remscheid, to provide a valve block comprising electrically controlled proportional displacement valves with pressure sensors which detect the pressure difference between pump delivery flow and maximum active load.
It is also known from German patent application P 42 41 848, which is not a prior publication, to use a pressure sensor in a controlled proportional valve, the pressure sensor converting the maximum load pressure into an electrical voltage signal.
The installation of sensors in the function-performing unit is not always without problems. Normally, not only do additional bores have to be made, through which the hydraulic fluid is able to reach the sensors or the vicinity of the sensors, seats for the sensors also have to be provided. Not only do these seats have be constructed so that the sensor has sufficient room, the sensor must normally also be safeguarded against being forced out of the housing again under the influence of the hydraulic pressure. On the other hand, the sensors are in many cases sensitive to damage. Such damage can easily occur as the function-performing unit is being assembled, that is, as the sensor is being installed in the function-performing unit.